Numerical study of flow structure (mixing process and reactivity) of diluted hydrogen non-premixed supersonic combustion system

Numerical simulation of supersonic combustion with transverse hydrogen injection is performed by solving the three-dimensional Favre-averaged Navier-Stokes equations coupled by the k - omega turbulence model. These equations are solved using an algorithm that is based on the third-order essentially nonoscillatory scheme. Several cases of the jet compositions (pure hydrogen and hydrogen diluted by nitrogen in 50:50 mol%) are considered to study the influence of the composition onto the structure and reactivity of the supersonic combustion systems. Seven step modified version of Spark model developed by Jachimowski is implemented to model chemical reaction of hydrogen combustion, which performs quite well in the considered relatively high temperatures. The simulation revealed that the jet penetration heights are equal for both cases, and the hydrodynamic fields looked similar except for the temperatures of the zones located ahead and behind the jet injection. The chemical reaction zone, indicated by OH radicals, was more intense for the pure hydrogen case, occupying a narrow region along the oblique shock wave line. In contrast, the use of a hydrogen/nitrogen jet mixture resulted in a significantly wider flame front zone. This suggests that the presence of nitrogen in the mixture diluted the hydrogen concentration, leading to slower combustion. The study shows that the flow properties and reactivity of the mixture significantly changing with the dilutions of the fuel composition.